P C BLOCKED - read why below Scam in operation.

I have just had my friend tell me that his computer has been blocked by the police and he has to pay £100 to get it unblocked within 72 hours or it will be perminantly blocked. Yes it is a scam but at his age he was totally lsot as it told him he had been looking at naughty sites when he hadn't, he was looking at a woodwork site when it came up.
The problem now is when he switches his computer on it is still there, the screen apprears frozen with no x to close it down.
Has anyone heard of this? How do i get back in to do a system restore and them a spywear clean etcetera. I was thinking of downloading soemthing like roadkill and taking it to him on a usb and seeing if that would work -any ideas?
I am sure lots of people would pay the money but luckily he told me first thinking he had to pay up.
The screen says something like 'Police central e-crime. PC blocked. Fine £100. pay by paysafe card. pc will be unblocked in 72 hours if you do or permanantly blocked if you don't pay' - or words to that affect, he couldn't remember it all.
Advise please.
E.

Have put hitman pro onto a usb drive but sine i don't know if his computer is 32 or 64 bits i dowbloaded both. how will i know which is his, the 32 or the 64?
Downloaded the maleware one too and will use on my computer now.

Have put hitman pro onto a usb drive but sine i don't know if his computer is 32 or 64 bits i dowbloaded both. how will i know which is his, the 32 or the 64?
Downloaded the maleware one too and will use on my computer now.

Start the rig and press F8 new screen follow to set my computer to an earlier time or words to that effect. Use the NSEW [arrow keys] keys on the key board to attain this press enter and merely wait and then allocate the date prior to this incident.

When completed employ a full anti virus and malware programmes and you should be clear.